In the past, suck back valves have been used for the purpose of preventing fluid in piping from dripping down from the end of the piping after a flow passage in the piping have been closed. As the suck back valves, ones with mechanisms for causing displacement of diaphragms to change the volumes in the valves and suck back fluid and ones such as disclosed in Japanese Unexamined Patent Publication No. 2003-254459 which are provided at the upstream sides of the suck back valves with diaphragm type on/off valves, integral with the suck back valves, for stopping the flow of fluid are most general. In the operation of such a latter valve, the on/off valve arranged at the upstream side is at first closed, and the suck back valve is then operated. Further, as described in Japanese Unexamined Patent Publication No. 2003-278927, there is also a system which uses a diaphragm and simultaneously operates the on/off valve and suck back valve.
In a conventional suck back valve of a type integral with an on/off valve, the on/off valve and the suck back valve are individually controlled, so there were the problems that it was difficult to match the timing of closing the on/off valve and the timing of operating the suck back, the predetermined amount of suck back could not be obtained, and dripping of fluid occurred. Further, not only was adjustment of the timing troublesome, but even after adjustment once, if the air pressure for operating the valve fluctuated, the timings of the closing of the on/off valve and the suck back operation became off. Therefore, there was the problem that frequent adjustment became necessary. Further, in the case of applications for coating photoresist solutions in semiconductor production, since an on/off valve using a diaphragm has a structure in which bubbles easily build up in the valve chamber, there was the problem of the built up bubbles flowing out and spreading over the wafer to cause uneven coating and thereby lower the yield. There was a similar problem even with a suck back valve using a diaphragm.